Fracturing one or more areas in a well to increase the productivity thereof, for example to increase the flow of oil and gas into the wellbore for production to the earth's surface, is well known and practiced daily. A conventional procedure in many fracturing processes is to inject a plurality of solid particles such as sand, gravel, and the like, into the fractures so that when the fracturing process is completed the fractures cannot reclose due to overburden pressure and thereby lose the benefit of enhanced fluid recovery due to the formation of the fractures. The propping agent particles flow into the fractures themselves and keep the fractures propped open in a porous manner so that produced fluids can flow through the fractures. The advantage of the fracturing procedure is therefore, retained so long as the propping agent remains in the fracture.
Sometimes, due to numerous and varied conditions, the propping procedure is not successful, or at best partially successful, in that the propping agent is actually forced by the produced fluids back out of the fracture and into the wellbore thereby allowing the fractures to reclose or at least partially reclose, and lose at least part of the benefit of the fracturing process. The produced propping agent is recovered at the earth's surface along with the produced fluids and this indicates that something is wrong with the fracture system that was originally designed for.
In such a situation it would be extremely helpful to be able to identify the particular propping agent which is being recovered at the earth's surface so as to better localize the area or areas where the fracturing process failed.